One extra wire allows transmission of triple the amount of electricity via three-phase power. With three wires rather than two, electrical operators can transmit triple the electricity. “Polyphase” is another term for three-phase power.
Three phase power usually transmits enormous amounts of electricity. These are the large transmission lines on tall polls. Electricity is converted into two-phase power, more practical for home use, at endpoint stations. Both heavy industry and electric cars use powerful three-phase induction engines.
Markedly, three phase power results in significant cost savings due to the reduced amount of wire needed.
Meters that regulated and measured the electricity spanned many patents. Eventually, Westinghouse acquired virtually all of them to compete with Edison, eventually lighting up the 1893 Chicago World’s Fair. Tesla’s patents proved to be the most valuable.